It would be difficult to overstate the importance that ICs have attained in today's electronic devices. They perform the core functions of computers, communications devices, automobiles, airplanes, thermostats, calculators and chemical plants, just to name a few widely diverse examples.
Given their importance and sheer numbers, the quest over the last several decades has been to make ICs smaller, more powerful, less expensive and less energy consumptive. To these ends, IC include larger numbers of devices (mostly transistors) in smaller sizes and greater densities. The progression has been from Large-Scale ICs (LSIs) to Very Large-Scale ICs (VLSIs) to ULSIs.
Electrical isolation is an important objective for many types of circuits, including those embodied as ICs. Isolation in its most basic sense occurs when at least DC voltages are contained to within a circuit (e.g., isolated power supplies). Isolation is extended in some cases to include power (e.g., voltage detectors) and even AC voltages (e.g., certain communications circuits).
The prior art contains several different devices that can bridge isolated circuits, allowing only AC voltages, power or signals to be conveyed as desired. These devices are broadly divided into two classes: passive and active.
Passive devices require no power for their own operation and include transformers (which use magnetic fields to bridge circuits) and capacitors (which use electric fields to bridge circuits). Active devices do require power to operate and include buffers (e.g., differential amplifiers, which block common mode electric signals and use only differential electric signals to bridge circuits) and optocouplers (which use light to bridge circuits).
Passive devices are advantageous in that they are simple and require no power for their own operation. However, transformers are by their nature relatively large and require a structure that does not easily lend itself to integration into an IC. Capacitors are smaller than transformers and are easily integrated into an IC, but must be sized inversely to the frequencies they are to convey—the lower the frequency, the larger the capacitor. This physical constraint renders them unsuitable for many applications.
Active devices are generally more flexible and can in some cases provide greater degrees of isolation, but they require power to operate and often take up larger areas on ICs. Active devices are disadvantageous in ICs where power consumption and size are critical.
The need for effective isolation in ICs, particularly ULSIs, remains unsatisfied. What is needed in the art is a fundamentally new electronic device that provides electrical isolation and is readily integrable into an IC.